Skip, The easiest way to determine the oven resistor values for an unmarked tube is to directly measure the oven temperature and select a resistance to set it at the temperature you want. Your tube is a STD tube so I'd set it at 90 degrees C. Take a thermocouple meter and thermocouple and cut the junction off the end of the thermocouple. Attach a couple tiny alligator clips or grabbers. Next look at the potting around where the tubes cables come out. You should see short stubs of two different color wires peeking out of the potting. These are the ends of a thermocouple connected directly to the oven housing! I can't remember which type thermocouple it is. (I'll look in my notes and at the meter I use and let you know!) Connect the wires to your meter matching the color of the wires. Now with the tube cold you should see the ambient temperature on the meter. Power up the unit and you will see the temp start to rise. It will stabilize at the point determined by the resistance you selected. If too hot increase the resistance if too cold decrease. Cheers, Corby

It would work as well if you used a pair of regular copper wires to connect the meter to the thermocouple... The junctions created by all the new connections will cancel out. Mike On 10/11/2016 20:53, cdelect@juno.com wrote: > Skip, > > The easiest way to determine the oven resistor values for an unmarked > tube is to directly measure the oven temperature and select a resistance > to set it at the temperature you want. > Your tube is a STD tube so I'd set it at 90 degrees C. > Take a thermocouple meter and thermocouple and cut the junction off the > end of the thermocouple. > Attach a couple tiny alligator clips or grabbers. > Next look at the potting around where the tubes cables come out. > You should see short stubs of two different color wires peeking out of > the potting. > These are the ends of a thermocouple connected directly to the oven > housing! > I can't remember which type thermocouple it is. (I'll look in my notes > and at the meter I use and let you know!) > Connect the wires to your meter matching the color of the wires. > Now with the tube cold you should see the ambient temperature on the > meter. > Power up the unit and you will see the temp start to rise. > It will stabilize at the point determined by the resistance you selected. > If too hot increase the resistance if too cold decrease. > > Cheers, > > Corby >

Well, they cancel if they're at the same temperature. Bill Hawkins -----Original Message----- From: Mike Millen Sent: Friday, November 11, 2016 12:28 AM It would work as well if you used a pair of regular copper wires to connect the meter to the thermocouple... The junctions created by all the new connections will cancel out. Mike

Quite true, of course. I was only anticipating a quick-&-dirty temperature check... I should have realised that q-&-d isn't in a Time-Nut's vocabulary. :-) Mike On 11/11/2016 06:39, Bill Hawkins wrote: > Well, they cancel if they're at the same temperature. > > Bill Hawkins > > -----Original Message----- > From: Mike Millen > Sent: Friday, November 11, 2016 12:28 AM > > It would work as well if you used a pair of regular copper wires to > connect the meter to the thermocouple... > > The junctions created by all the new connections will cancel out. >

On 11/10/16 10:28 PM, Mike Millen wrote: > It would work as well if you used a pair of regular copper wires to > connect the meter to the thermocouple... > > The junctions created by all the new connections will cancel out. > as long as the temperatures are "exactly" the same, (Seebeck coefficient varies with temperature) and the two metals at the junctions are the same, (ditto, but the curves are different for different materials) and the mechanical configuration is the same (current density also affects it) For run of the mill "measure to 1 degree at room temperature" you can probably make that assumption. But if you're looking for precision, you need to take this stuff into account (that's what "cold junction compensation" is all about.. )

Hi > On Nov 11, 2016, at 8:02 AM, jimlux <jimlux@earthlink.net> wrote: > > On 11/10/16 10:28 PM, Mike Millen wrote: >> It would work as well if you used a pair of regular copper wires to >> connect the meter to the thermocouple... >> >> The junctions created by all the new connections will cancel out. >> > > as long as the temperatures are "exactly" the same, > (Seebeck coefficient varies with temperature) > and the two metals at the junctions are the same, > (ditto, but the curves are different for different materials) > and the mechanical configuration is the same > (current density also affects it) The gotcha is that few of us weld copper directly to the thermocouple leads. The far more common approach is to grab clip leads. At least around here, the clips on the leads are not made of copper. They are some sort of (badly worn) plating over (oxidized) base material. I grab a “copper wire” clip lead and hook up to the thermocouple. There isn’t a lot of delta T in most bench situations. In this case you have a heated gizmo warming things up …. Who knows what the delta T may be or how small the contact area actually is. Simple answer: Don’t trust the first number you get. Try it a couple of times with *different* leads. Make sure you do indeed get within a degree or three on each of them. Depending on how you have your cold junction set up, that may also need the same treatment. Bob > > > For run of the mill "measure to 1 degree at room temperature" you can probably make that assumption. > > But if you're looking for precision, you need to take this stuff into account (that's what "cold junction compensation" is all about.. ) > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there.

If you want sub degree precision, you will need to make your connections to dissimilar metals on an isothermal boundary, a terminal block is better than clips in free air. On Fri, Nov 11, 2016 at 8:28 AM, Bob Camp <kb8tq@n1k.org> wrote: > Hi > > > On Nov 11, 2016, at 8:02 AM, jimlux <jimlux@earthlink.net> wrote: > > > > On 11/10/16 10:28 PM, Mike Millen wrote: > >> It would work as well if you used a pair of regular copper wires to > >> connect the meter to the thermocouple... > >> > >> The junctions created by all the new connections will cancel out. > >> > > > > as long as the temperatures are "exactly" the same, > > (Seebeck coefficient varies with temperature) > > and the two metals at the junctions are the same, > > (ditto, but the curves are different for different materials) > > and the mechanical configuration is the same > > (current density also affects it) > > The gotcha is that few of us weld copper directly to the thermocouple > leads. The far more > common approach is to grab clip leads. At least around here, the clips on > the leads are > not made of copper. They are some sort of (badly worn) plating over > (oxidized) base > material. > > I grab a “copper wire” clip lead and hook up to the thermocouple. There > isn’t a lot of > delta T in most bench situations. In this case you have a heated gizmo > warming things up …. > Who knows what the delta T may be or how small the contact area actually > is. > > Simple answer: Don’t trust the first number you get. Try it a couple of > times with *different* > leads. Make sure you do indeed get within a degree or three on each of > them. Depending on > how you have your cold junction set up, that may also need the same > treatment. > > Bob > > > > > > > > For run of the mill "measure to 1 degree at room temperature" you can > probably make that assumption. > > > > But if you're looking for precision, you need to take this stuff into > account (that's what "cold junction compensation" is all about.. ) > > > > _______________________________________________ > > time-nuts mailing list -- time-nuts@febo.com > > To unsubscribe, go to https://www.febo.com/cgi-bin/ > mailman/listinfo/time-nuts > > and follow the instructions there. > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/ > mailman/listinfo/time-nuts > and follow the instructions there. >

Hi Even *with* all the fancy stuff in my Fluke thermometers … they still are only rated for a bit worse than 0.1 C. When I send them in for calibration, the thermometer generally comes back “calibrated fine”. The thermocouple I send in with them often comes back with a note about “you need to buy a real thermocouple …”. On a simple lash up, you would use a thermocouple that is lying around as your cold junction. If you get yours from eBay (like I do) … who knows what you have. Lots of gotcha’s. Bob > On Nov 11, 2016, at 9:16 AM, Scott Stobbe <scott.j.stobbe@gmail.com> wrote: > > If you want sub degree precision, you will need to make your connections to > dissimilar metals on an isothermal boundary, a terminal block is better > than clips in free air. > > On Fri, Nov 11, 2016 at 8:28 AM, Bob Camp <kb8tq@n1k.org> wrote: > >> Hi >> >>> On Nov 11, 2016, at 8:02 AM, jimlux <jimlux@earthlink.net> wrote: >>> >>> On 11/10/16 10:28 PM, Mike Millen wrote: >>>> It would work as well if you used a pair of regular copper wires to >>>> connect the meter to the thermocouple... >>>> >>>> The junctions created by all the new connections will cancel out. >>>> >>> >>> as long as the temperatures are "exactly" the same, >>> (Seebeck coefficient varies with temperature) >>> and the two metals at the junctions are the same, >>> (ditto, but the curves are different for different materials) >>> and the mechanical configuration is the same >>> (current density also affects it) >> >> The gotcha is that few of us weld copper directly to the thermocouple >> leads. The far more >> common approach is to grab clip leads. At least around here, the clips on >> the leads are >> not made of copper. They are some sort of (badly worn) plating over >> (oxidized) base >> material. >> >> I grab a “copper wire” clip lead and hook up to the thermocouple. There >> isn’t a lot of >> delta T in most bench situations. In this case you have a heated gizmo >> warming things up …. >> Who knows what the delta T may be or how small the contact area actually >> is. >> >> Simple answer: Don’t trust the first number you get. Try it a couple of >> times with *different* >> leads. Make sure you do indeed get within a degree or three on each of >> them. Depending on >> how you have your cold junction set up, that may also need the same >> treatment. >> >> Bob >> >> >>> >>> >>> For run of the mill "measure to 1 degree at room temperature" you can >> probably make that assumption. >>> >>> But if you're looking for precision, you need to take this stuff into >> account (that's what "cold junction compensation" is all about.. ) >>> >>> _______________________________________________ >>> time-nuts mailing list -- time-nuts@febo.com >>> To unsubscribe, go to https://www.febo.com/cgi-bin/ >> mailman/listinfo/time-nuts >>> and follow the instructions there. >> >> _______________________________________________ >> time-nuts mailing list -- time-nuts@febo.com >> To unsubscribe, go to https://www.febo.com/cgi-bin/ >> mailman/listinfo/time-nuts >> and follow the instructions there. >> > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there.

Hello to the group. I somewhat suspect we have veered way off the track on the thread or the thread changed and I missed it. Typical of me. Useful comments on Tcouples and wires. But with respect to the start of the subject of unmarked CS tubes easily a 5 or more degree range is fine. You can adjust up or down after you are in range for optimum performance or life as a trade off. Granted you may not actually know what the temperature is to 1 degree. But on an unknown tube its a great place to start. As an example Frankenstein runs 10 C hot approx. It resulted in some fumes of C and I beam. When I started Frankenstein it would have been good to know it was a Tcouple and it should have been an obvious guess. I was just reading and matching voltage outputs after the bridge. Regards Paul WB8TSL On Fri, Nov 11, 2016 at 9:16 AM, Scott Stobbe <scott.j.stobbe@gmail.com> wrote: > If you want sub degree precision, you will need to make your connections to > dissimilar metals on an isothermal boundary, a terminal block is better > than clips in free air. > > On Fri, Nov 11, 2016 at 8:28 AM, Bob Camp <kb8tq@n1k.org> wrote: > > > Hi > > > > > On Nov 11, 2016, at 8:02 AM, jimlux <jimlux@earthlink.net> wrote: > > > > > > On 11/10/16 10:28 PM, Mike Millen wrote: > > >> It would work as well if you used a pair of regular copper wires to > > >> connect the meter to the thermocouple... > > >> > > >> The junctions created by all the new connections will cancel out. > > >> > > > > > > as long as the temperatures are "exactly" the same, > > > (Seebeck coefficient varies with temperature) > > > and the two metals at the junctions are the same, > > > (ditto, but the curves are different for different materials) > > > and the mechanical configuration is the same > > > (current density also affects it) > > > > The gotcha is that few of us weld copper directly to the thermocouple > > leads. The far more > > common approach is to grab clip leads. At least around here, the clips on > > the leads are > > not made of copper. They are some sort of (badly worn) plating over > > (oxidized) base > > material. > > > > I grab a “copper wire” clip lead and hook up to the thermocouple. There > > isn’t a lot of > > delta T in most bench situations. In this case you have a heated gizmo > > warming things up …. > > Who knows what the delta T may be or how small the contact area actually > > is. > > > > Simple answer: Don’t trust the first number you get. Try it a couple of > > times with *different* > > leads. Make sure you do indeed get within a degree or three on each of > > them. Depending on > > how you have your cold junction set up, that may also need the same > > treatment. > > > > Bob > > > > > > > > > > > > > For run of the mill "measure to 1 degree at room temperature" you can > > probably make that assumption. > > > > > > But if you're looking for precision, you need to take this stuff into > > account (that's what "cold junction compensation" is all about.. ) > > > > > > _______________________________________________ > > > time-nuts mailing list -- time-nuts@febo.com > > > To unsubscribe, go to https://www.febo.com/cgi-bin/ > > mailman/listinfo/time-nuts > > > and follow the instructions there. > > > > _______________________________________________ > > time-nuts mailing list -- time-nuts@febo.com > > To unsubscribe, go to https://www.febo.com/cgi-bin/ > > mailman/listinfo/time-nuts > > and follow the instructions there. > > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/ > mailman/listinfo/time-nuts > and follow the instructions there. >